The subject matter disclosed herein relates to the fabrication and use of radiation detectors, including X-ray radiation detectors composed of arrays of CMOS tiles.
Non-invasive imaging technologies allow images of the internal structures or features of a subject (patient, manufactured good, baggage, package, or passenger) to be obtained non-invasively. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of X-rays through the target volume or the reflection of acoustic waves, to acquire data and to construct images or otherwise represent the internal features of the subject.
By way of example, digital X-ray imaging systems are used to generate digital data in a non-invasive manner and to reconstruct such digital data into useful radiographic images. In current digital X-ray imaging systems, radiation from a source is directed toward a subject or object, typically a patient in a medical diagnostic application, a package or baggage in a security screening application, or a fabricated component in an industrial quality control or inspection application. A portion of the radiation passes through the subject or object and impacts a detector. The scintillator of the detector converts the higher-energy X-ray radiation to lower-energy light photons that are sensed using photo-sensitive components (e.g., photodiodes or other suitable photodetectors). The detector is typically divided into a matrix of discrete picture elements or pixels, and encodes output signals based upon the quantity or intensity of the radiation impacting each pixel region. The signals may then be processed to generate an image that may be displayed for review.
The detector features may be based on or formed from a silicon semiconductor substrate. Such a silicon substrate may be provided as crystalline silicon (c-Si), which consists of an ordered silicon matrix (e.g., a well ordered crystal lattice), or amorphous silicon (a-Si), which does not have an ordered matrix (e.g., a random crystal lattice). The random crystal lattice of a-Si typically provides a much lower electron mobility than that provided by an ordered crystal lattice of c-Si (e.g., <1 cm2/(v·s) compared to approximately 1,400 cm2/(v·s)). Despite this, the mainstream technology for fabricating X-ray panels for medical and industrial inspection utilizes amorphous silicon TFTs due to their competitive cost and large area capability. In particular, X-ray panels for medical and industrial inspection often require large area image sensors, typically ranging from 20 cm×20 cm to 40 cm×40 cm and more, and such large sensors can typically be made using a-Si technology more readily than using c-Si technology.
However, in some applications there is a growing need to build panels with higher resolution and lower electronic noise than may be achievable with a-Si technology. Because of the higher electron mobility associated with c-Si the size of features that can be formed using c-Si can be much smaller than those formed from the a-Si. Thus, X-ray detectors based on c-Si technology, such as those employing complementary metal-oxide-semiconductors (CMOS) formed from c-Si, may outperform traditional a-Si based X-ray detector in various ways. However, disadvantages of using c-Si include: higher cost and smaller panel size due to limitations in the practical size of silicon wafers used to fabricate c-Si devices. Such wafer size limitations may require tiling multiple, smaller panels together to form a detector panel of useful size. However, such tiling arrangements introduce complexities in the electrical interconnection arrangements needed to operate (e.g., readout) such a detector panel and may be difficult or impractical to implement in practice.